An organised stock-rustling ring is stealing tens of thousands of dollars of stud rams, ewes and lambs from remote properties in the Cheviot region of North Canterbury, police say.

The thefts are being committed at full moon, eliminating the need for light and heading dogs.

Constable Brian Dewes, of Cheviot police, is urging farmers and others in the rural area to report suspicious vehicles and suspicious behaviour without delay.

Nearly 1000 head of stock have disappeared from sheep runs in the past three years.

"What I require from farmers in any rural area is that they report suspicious vehicles, registration numbers and suspicious people, because they are our eyes and ears," Dewes said.

The group is targeting isolated areas accessible by trucks - and the time to be "extra-vigilant" was full moon, he said.

"It's the same crowd, from my experience. They're very organised and they've been doing it for some time."

Farm equipment was also being taken.

Stock losses in the three years to early 2013 - the most recent figures available - have been substantial. They included 266 ewes valued at $42,000, 100 ewes in lamb, 400 lambs from another property, and 10 high-value perendale stud rams.

Stock rustling was reportedly costing the farming community about $120 million a year.

"These are massive sums for red meat farmers who are already struggling against a backdrop of the New Zealand dollar and difficult market conditions," she said.

Worse, a stolen animal may have been specifically bred from a line of genetics, making it "pretty much" irreplaceable.

Milne, who farms at Rotomanu on the West Coast, is asking farmers to report rustling, rural crime and cannabis finds on their land using online tools such as Stop Stock Theft.

Hidden cameras and covert electronic beeper devices to thwart raiders are now being trialled on some big blocks

Canterbury runholders and farmers are not the only ones hit. Last year, Hawke's Bay blocks were under siege from poachers and rustlers, with police worried that it would not be just sheep, cattle or deer in their sights.

"We do have a problem and that is our main fear because a lot of these people are carrying guns and knives," a police spokesman said.